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Homework Help: Smith Chart question

  1. Mar 17, 2014 #1
    1. The problem statement, all variables and given/known data
    A lossless transmission line has a characteristic impedance Z0 = 300 ohms, is 5.3 wavelength long, and is terminated in a load impedance ZL = 35 + j 25 (ohms). Find the following using Smith chart.

    a) The input impedance on the line
    b) The standing wave ration on the main line.
    c)If the load current is 1A, calculate the input power to the line.

    2. Relevant equations

    3. The attempt at a solution

    a) Zin = 300(6.2 - j4.5) = 1860 - j1350 (ohms)
    b) swr = 9.5
    c) I am not finding a good equation to calculate part C and not sure how you can extract this information from the chart. P= i^2 R => 35W to the load then the input would need to be 35 /0.8^2= 54.6875W
  2. jcsd
  3. Mar 19, 2014 #2
    So i can get VL = 35+j25(V)

    Vl = V0+(1+gamma)
    V0+ = 19.44+j13.89(v)

    Vin = V0+(exp(-j0.6pi) + 0.8exp(j0.6pi))
    Vin = 18.89+j13.70

    Iin = Vo+/Zo(exp(-j0.6pi) - 0.8exp(j0.6pi)
    Iin = -1.12-j33.29
    Iin* = -1.12+j33.29

    Pav = 0.5*Re(VI*)
    then i get -242W (this does not seem correct)

    Am i getting close?
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